Often, it is desired to make changes to the flow of current to and from electronic devices. For instance, it is required to make engineering or wiring changes between interconnected electronic devices. Such changes can, for example, include altering the wiring path between an integrated circuit chip and a circuit board or card to which it is attached.
Devices known as interposers act as intermediate structures between, for instance, an integrated circuit chip mounted on a chip carrier and a circuit board. An interposer typically includes at least one conductive plane sandwiched between two dielectric planes. The conductive plane typically includes a pattern of circuitry. A plurality of plated through holes are formed through the planes of the interposer so that the pattern of plated through holes formed on one surface of the interposer matches the pattern of ground, power and signal sites on the chip carrier; and the pattern of plated through holes on-the opposite side of the interposer matches the pattern of ground, power, and signal sites on the circuit board or card.
The circuitry in the conductive plane of the interposer provides connections between the chip carrier and the circuit board. Therefore, the interposer can provide connections between circuit boards and chips having different patterns of ground, power, and signal sites without requiring significant alteration of the circuit board or chip or chip carrier. This can save money by not requiring a separate circuit board for each type of chip and could allow a chip and or carrier to be removed from one circuit board and attached to another with relative ease. An interposer can also alter the function of a chip without requiring redesign of the chip or chip carrier.
It may also become necessary to modify the internal circuitry of a chip or card to correct defective lines or vias or to make changes in the basic circuitry to accommodate design changes to upgrade an electronic package or to modify a package use with different devices, for example. An interposer can correct such defects and make such changes. Furthermore, an interposer may also eliminate problems associated with chips mounted on circuit boards having a different coefficient of thermal expansion.
In another effort to make changes in the function of an electronic package, attempts have been made to incorporate electronic circuit components within the structure of a circuit board. Such components could act similarly to an interposer.